feat: add alembic migrations and PostgreSQL CI support

- Add alembic dependency and initialize migration framework
- Configure async alembic env.py for SQLAlchemy 2.0
- Create initial migration for PostORM table
- Gate init_db() with SKIP_INIT_DB env var for CI/production
- Add PostgreSQL service to Woodpecker CI pipeline
- Create integration tests for migrations (TC-INT-001..002)
- Create integration tests for SQLAlchemyPostRepository (TC-INT-003..009)
- Add unit test for init_db skip behavior (TC-UNIT-901)
- All 176 tests pass, coverage 72.59%

.woodpecker/pipeline.yml

@@ -2,6 +2,14 @@ when:
   event: [push, pull_request]
   branch: [dev, main, master]
 
+services:
+  - name: postgres
+    image: postgres:17-alpine
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: blog_test
+
 steps:
   - name: deps
     image: python:3.13
@@ -71,6 +79,21 @@ steps:
       - pip install uv
       - uv run --no-sync pytest tests/unit/
 
+  - name: test-integration
+    image: python:3.13
+    volumes:
+      - /tmp/uv-cache:/root/.cache/uv
+    environment:
+      UV_CACHE_DIR: /root/.cache/uv
+      UV_LINK_MODE: copy
+      UV_PYTHON: "3.13"
+      DB_URL: postgresql+asyncpg://postgres:postgres@postgres:5432/blog_test
+      SKIP_INIT_DB: "1"
+    depends_on: [deps]
+    commands:
+      - pip install uv
+      - uv run --no-sync pytest tests/integration/ -v
+
   - name: test-e2e
     image: python:3.13
     volumes:
@@ -79,9 +102,12 @@ steps:
       UV_CACHE_DIR: /root/.cache/uv
       UV_LINK_MODE: copy
       UV_PYTHON: "3.13"
+      DB_URL: postgresql+asyncpg://postgres:postgres@postgres:5432/blog_test
+      SKIP_INIT_DB: "1"
     depends_on: [deps]
     commands:
       - pip install uv
+      - uv run --no-sync alembic upgrade head
       - apt-get update && apt-get install -y libnss3 libnspr4 libatk1.0-0 libatk-bridge2.0-0 libcups2 libdrm2 libxkbcommon0 libxcomposite1 libxdamage1 libxfixes3 libxrandr2 libgbm1 libasound2
       - uv run --no-sync playwright install chromium
       - uv run --no-sync blog &